Naphthalene hydrogenation



Nov. 17, 1970 H QNQHIcKSQ JR, ETAL 3541,"!

NAPHTHALENE HYDROGENATION Filed Jan. 9, 1968 Q j INVENTORS HAROLD N.HICKS JR. 83 v ANDREW E. HAILE ATTORNEY United States Patent 01 fice3,541,169 Patented Nov. 17, 1970 3,541,169 NAPHTHALENE HYDROGENATIONHarold N. Hicks, Jr., Huntington, W. Va., and Andrew E.

Haile, Ashland, Ky., assignors to Ashland Oil & Re-

fining Company, Houston, Tex., a corporation of Kentucky Filed Jan. 9,1968, Ser. No. 696,649 Int. Cl. C07c 5/10 US. Cl. 260-667 13 ClaimsABSTRACT OF THE DISCLOSURE A process for selectively hydrogenatingnaphthalene to substantial quantities of high purity Tetraline whichincludes: mixing a naphthalene feed material, preferably the naphthaleneproduct of a hydrodealkylation reaction, with hydrogen at ahydrogen-to-hydrocarbon ratio adapted to maintain vapor phase conditionsat the hereinafter-mentioned steps, preferably between about 6 and 25 to1; preheating the mixture to a temperature sufiicient to vaporize thenaphthalene feed, preferably between about 375 and 450 F; passing themixture through a chemisorptive solid material, preferably copper oxidedeposited on an inert carrier in an amount of about 10 to for exampleabout 20%, to remove sulfur contaminants from the feed mixture, passingthe clarified feed mixture through a plurality of adiabatic catalyticreactors, for example between 4 and 7, each followed by a separatecooling unit, without intermediate separation of the products, underconditions to maintain a pressure of about 20 to 100 p.s.i.g., a nominalreactor temperature of about 400-550" F., a weight hourly space velocityof about 0.5 to 2.5, and a temperature rise through any one of saidreactors not exceeding between about 50 and 100 F., and whilemaintaining in the catalytic reactors a sulfur-sensitive hydrogenationcatalyst, preferably nickel oxide, in an amount of about 0.5 to byweight, and preferably 10%, on an inert support; said conditions ofhydrogenation and operation of said adiabatic reactors also beingselected to convert a major portion of the naphthalene feed, preferablyat least 80% of the naphthalene, to Tetralin; passing the product fromthe last cooling unit to an isothermally operated catalytichydrogenation reactor, preferably containing the same catalyst as theadiabatic reactors; separating unreacted hydrogen from the product ofthe isothermal reaction, preferably recycling the hydrogen to the feed,and stabilizing the liquid product to remove about 5% thereof as anoverhead and recover a bottoms product comprising Tetralin of highpurity.

SUMMARY OF THE PRIOR ART T etralin without the concomitant production ofDecalin, pleasant smelling liquid which is non-poisonous, non-explosive,and practically non-inflammable. In fact, experiments have shown thateven with a considerable internal dosage, only slight toxic symptoms areobserved. It is an excellent solvent and thinner, particularly forpaints, varnishes and the like since it will leave no residue uponevaporation, thus causing no discoloration, even with white lacquers. Inaddition, Tetralin has an almost unbelievable variety of uses. Forexample, it may serve as a solvent for waxes, resins, rubber, gums,oils, resinates, cellulose ethers, asphalt, linoxyn, liquid driers,metallic soaps, greases, benzene, toluene, naphthalene, casingheadgasoline and other products. It is also useful in removing printing inkfrom paper and as a substitute for turpentine. It can also be used forpurifying coal gas, for extracting sulfur from spent oxides in gaspurification, and as a component of paints, varnishes, bituminousemulsions, waterproofing compositions, motor fuels, paint and varnishremovers in textile processing, in agricultural sprays, in shoe andfloor polishes, etc. It also has use in extracting casinghead gasolinefrom natural gas, in extracting liquids from normally solid carbonaceousmaterials, such as coal, and many other allied uses.

In spite of the value and many uses of Tetralin, there are presentlyonly limited commercial supplies of this material. There are severalreasons for such limited production.

While the classic process for the production of Tetralin is thehydrogenation of naphthalene in the presence of a catalyst at about 300R, such production is an expensive and complex proposition. One of themajor problems involved is the catalyst system. Since most naphthalenestreams contain small amounts of contaminants, particularly sulfur, onemajor problem in the production of Tetralin by the hydrogenation ofnaphthalene is the catalyst system. Most conventional hydrogenationcatalysts are sulfur-sensitive and thus have an extremely short lifewhile operating on available naphthalene streams. Further, it is mostdiificult in these systems to produce high purity Tetralin without theconcomitant production of Decalin, and the consequent requirement ofvery precise fractionation to separate the two. Previous investigatorshave studied numerous catalytic systems for the production of Tetralin.However, all of these efiorts have eventually reached theselectivity-catalyst life impasse. For example, numerous patents claimthe production of about Tetralin and 20% Decalin and good catalyst life,but none disclose a process which appears to be capable of producingsubstantially pure Tetralin with only minor percentages of Decalin orunconverted naphthalene. Another alternate is, of course, the use ofsulfur-resistant catalysts, but there are more expensive and none areknown which are selective to Tetralin.

The majority of the prior art systems have also suffered thedisadvantages of operating as a liquid system rather than in the vaporphase. The man advantages of operating any reaction in the vapor stateas opposed to the liquid state are well known.

Further, with one known exception, all of the prior art techniques areincapable of operating to obtain high yields of Tetralin in a singlepass system. This one exception is a liquid phase, sodium catalyzedtechnique presently practiced on a commercial scale. This techniquetreats a coal tar naphthalene with a quinoline-promoted sodium catalystat an operating pressure of about 1000 to 3000 p.s.i.g. However, thisprocess suffers from a relatively poor yield (about based on thenaphthalene feed. Further, direct and indirect operating costs areextremely high due to the high cost of the catalyst and the highinvestment associated with the high operating pressures and the largereactor volumes required.

The major advantage of the sodium-catalyzed naphthalene hydrogenationprocess lies in the ability of this process to use a relatively impurenaphthalene feed. For example, coal tar naphthalene, as opposed topetroleum naphthalene, may be utilized. As a result, this is generallythe sole source of Tetralin. In addition, production of phthalicanhydride is growing at such a rate that it requires substantially thewhole of the petroleum naphthalene production ans, for economic reasons,increasing quantities of coal tar naphthalene. This composition, fromphthalic anhydride manufacture, is further complicated by the supply ofcoal tar naphthalene continuously decreasing. The latter is due largelyto improvements in blast furnace operation and the consequent decline inmetallurgical coke requirements. The net result is that coal tarnaphthalenes are continuing to decrease in spite of an increasingdemand. In addition, processes for producing coal tar naphthalene arestill relatively inefficient and do not recover high percentages ofnaphthalene. The sum and substance of all these factors is that there isa definite need for a process for the production of high yields ofTetralin from petroleum naphthalene, as well as a process which issimple and economical.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an improved process for the hydrogenation ofaromatics which overcomes the problems enumerated above. A furtherobject of the present invention is to provide an improved process forthe hydrogenation of naphthalene. Yet another object of the presentinvention is to provide an improved process for the selectivehydrogenation of naphthalene to Tetralin. Another ob ect of the presentinvention is to provide an impreved process for the production ofTetralin in carbon steel equipment. A further object of the presentinvention is to provide an improved process for the production ofTetralin in high yields. Yet another object of the present invention isto provide an improved process for the production of Tetralin in thepresence of a low-cost, commercially available catalyst. Another andfurther object of the present invention is to provide an improvedprocess for the production of Tetralin in which catalyst life islengthened. Another and further object of the present invention is toprovide an improved process for the production of Tetrahnun which theselectivity of the catalyst for Tetralin 13 maintained extremely high.Another and further object of the present invention is to provide animproved process for the production of Tetralin wherein the feedmaterlals are pretreated to remove contaminants. Yet another ob ect ofthe present invention is to provide an lmproved process for theproduction of Tetralin wherein an improved adsorbent for feedcontaminants is utilized. Another and further object of the presentinvention is to provide an improved process for the production ofTetralin which utilizes a single-pass reactor system. A still further obect of the present invention is to provide an improved process for theproduction of Tetralin which ut111zes a slnglepass adiabatic reactorsystem with no intermediate fractionation. Another and further object ofthe present invention is to provide an improved process for theproduction of Tetralin wherein the reaction is carried out to apredetermined degree of conversion in an aditbatic reactor system andthereafter, is carired to substantially complete conversion in anisothermal reactor. Another object of the present invention is toprovide an lmproved system for the production of Tetralin where1nrelat1vely low temperatures are employed. Yet another ob ect of thepresent invention is to provide an improved process for the vapor phasereaction of hydrogen and naphthalene to produce Tetralin. A stillfurther object of the present invention is to provide an improvedprocess for the production of Tetralin wherein plug flow is maintainedthrough the reaction system.

Briefly in accordance with the present invention, it has been found thatnaphthalene can be selectively converted to substantial quantities ofTetralin by hydrogenating the naphthalene in a plurality of seriallyconnected reaction zones at least one of the reaction zones beingoperated under adiabatic conditions and at least one of the otherreaction zones being operated under isothermal conditions. It has alsobeen found that maintaining a vapor phase throughout the reaction andmaintaining a temperature below about 550 F. contributes greatly to theselectivity of the reaction and the catalyst life. Further, it has beenfound that sulfur-sensitive hydrogenation catalyst may be utilized inthe reaction by first passing the feed material through a body of aparticulate material comprising, copper oxide deposited on a solid inertsupport.

A better understanding of the present invention will be obtained fromthe following detailed description of the preferred embodiment when readin conjunction with the single sheet of drawings, which drawing is aflow diagram of the preferred system of the present invention.

In accordance with the figure of the drawings, the naphthalene feed ispreferably obtained by hydrodealkyla- '4 tion of desulfurized, dicyclicconcentrates, as from hydrodealkylation unit 10. The naphthalene ispassed through line 12 to preheater 14. Preheatcr 14 may take a varietyof forms, including indirect heating with hot oil, as by passing hot oilthrough line 16. In addition to or in place of preheater 14, the feedmay be preheated by indirect exchange with the product of the system bypassing the feed through line 20 and thence back to line 12. Hydrogenfeed is introduce to the system through line 22. The preheated reactantsare passed through one of two downflow, chemisorption guard cases, 24 or26 by Way of lines 28 and 30, respectively. As pointed out elsewhere,these guard cases serve to remove catalytic poisons from the feed. Theclarified feed is discharged from guard cases 24 or 26 through lines 32or 34, respectively. The guard cases may, of course, be switched forregeneration when breakthrough of the heteroatoms which are to beremoved by the guard cases occurs. Such breakthrough is generallyevidenced by a rapid decline in the temperature rise across reactor 36.Reactor 36 is the first of a series of fixed-bed adiabatic, catalytichydrogenation units. The product of the first adiabatic reactor 36 isdischarged through line 38 to a cooler 40. The product of cooler 40 hashad the heat of reaction from reactor '36 essentially removed so thatthe feed to adiabatic reactor 38 will be the same temperature as that tothe previous reactor 36. Product from cooler 40 is discharged throughline 42 to a second fixed-bed hydrogenation reactor 44. The product ofhydrogenation reactor 44 is likewise discharged through line 46 tocooler 48 where it is cooled and discharged through line 50 to a thirdhydrogenation reactor 52. From hydrogenation reactor 52, the product isdischarged through line 54 to cooler 56. From cooler 56 product passesthrough line 58 to fourth catalytic reactor 60. The product of reactor60 passes through line 62 to cooler 64 and then thrugh line 66 to afifth catalytic reactor 68. Catalytic reactor 68 is operated as anisothermal unit and is preferably of tube and shell construction withthe catalyst in the tubes and a boiling liquid in the shell. As shown inthe drawing, coolers 40, 48, '56 and 64 and the shell of the isothermalreactor 68 may be connected in parallel with a larger heat exchange 70.Thus, the coolers 40, 48, 56 and 64 and shell 68 would be used togenerate vapors of Dowtherm or other cooling material which would bedischarged through lines 72, 74, 76, 78 and 80, respectively, andfinally passed through line "82 to exchange 70. Exchanger can bestoperate as a steam generator. The steam would be discharged through line-84 for other use while the condensed cooling liquid or Dowthermcondensate would be discharged through line 86 and fed back to thecoolers through lines 88 90, 92, 94 and 96, respectively. Many otherexchanger systems could accomplish the same result without deviatingfrom the intended purpose of the present invention, which is to maintainthe average reactor temperature at values which enhance reactionselectivity to Tetralin, while at the same time converting the heat ofhydrogenation to useful energy (steam) in a highly eflieient andinexpensive system. The product of isothermal reactor 68 is dischargedthrough line 98 and preferably passes, in indirect heat exchange,through heat exchanger 18 to preheat the feed. From the heat exchangerthe product passes through line 100 to a high-pressure flash unit orseparator 102. In separator 102, unreacted hydrogen is separated andrecycled through line 104, recycle compressor 106, and line 108 tohydrogen feed line 22. A slip stream of the recycle hydrogen or all ofthe same may be purged through line 110 to a unit, not shown, for theremoval of hydrocarbon gases. The liquid fraction from separator 102 isdischarged through line 112 to a low-pressure flash unit or separator114. Hydrogen separated from the product in separator 114 is dischargedthrough line 116 for recycle and/or purge as previously pointed out. Theliquid product from separator 114 is, in turn, discharged through line118 to a product stabilization system. The product in line 118 is firstheated in a preheater 120, supplied with hot oil or other heatingmaterial through line 122. The heated material is passed through line124 to stabilizer 126. In product stabilizer 126, dissolved hydrogen andother light gases, small amounts of benzene and cyclohexane formed inthe reactors by hydrocracking, and small amounts of Decalin which areremoved through line 128, through a condenser 130, line 132 andaccumulator 134. From accumulator 134, gases are discharged for use asfuel or the like through line 136. Light liquids are discharge throughline 138 from whence all or a part thereof may be recycled to thestabilizer through line 140 or discharged through line 142. Stabilizerbottoms, comprising Tetralin of 95% or higher purity is dischargedthrough line 144 to Tetralin storage unit 146. The major contaminants ofthe Tetralin include naphthalene and Decalin.

As shown in the drawing, the preferred source of naphthalene, inaccordance with the present invention, is the naphthalene product of ahydrodealkylation unit. The hydrodealkylation unit may be operated on avariety of feed materials from any source of carbonaceous material,including, coal, petroleum, etc. For example, coke oven or coal tar oilsderived from carbonization of coal, liquids, extracted from coal bysolvent extraction with Tetralin, Decalin, etc., and liquids obtained bycombinations of solvent extraction and carbonization may be utilized.The feed material to the hydrodealkylation unit may also be a processstream from a petroleum or coal refinery such as catalytic reformate,obtained by contacting petroleum or coal liquids with a precious metalcatalyst, such as platinum, at a temperature of about 900-950" F., apressure of about 200 to 600 p.s.i.g., a weight hourly spacevelocitybetween about 1.5 and and a hydrogen-tohydrocarbon ratio betweenabout 3 to l and to 1. A higher-boiling reformate fraction, boilingbetween about 400-600 F. is preferred. Still another feed for thehydrodealkylation reaction may include a reformer product, boilingbetween about 400-600" R, which has been subjected to solvent extractionsuch as by the UDEX. process (triethylene glycol and water). Otherpetroleum fractions which may be used as feed materials includekerosene, which has been extracted with an aromatic selective solvent,such as sulfur dioxide, a catalytic cracked light cycle oil which hasbeen subjected to solvent extraction, as 'with sulfur dioxide, or acatalytic cracked light cycle oil which has been subjected tohydroocracking. The hydrodealkylation unit is preferably a catalyticunit, for example utilizing a catalyst containing 10 to chromia on gammaalumina. A highly effective catalyst of this type is designated 6-41 byits manufacturer, the Girdler Construction Company, Louisville, Ky. Byutilizing such a catalyst, the hydrodealkylation may be carried out attemperatures between about 1000 and 1400 -F., and preferably between1200-1400 F.; at a Weight hourly space velocity between about 0.5 and 5,and preferably between 0.5 and 3; and at a hydrogen-to-hydrocarbon ratiobetween about 2 to 1 and 30 to 1, and preferably between 10 to 1 andto 1. It is possible to carry out the hydrodealkylation without acatalyst, in which case the temperature is maintained above about 1200F., the pressure above about 500 p.s.i.g., and thehydrogen-to-hydrocarbon ration between about 14,000 and 19,000 cubicfeet of hydrogen per barrel of feed.

In a hydrodealkylation unit, the feed is desulfurized to a certainextent and monocyclic and polycyclic aromatics dealkylated to producevaluable benzene, toluene, xylenes and naphthalene. The product of thehydrodealkylation unit includes a normally gaseous material and anormally liquid material. The residual light gases are drawn off andused as a plant fuel. The liquid fraction is then separated into adealkylated fraction containing benzene, toluene, xylenes and/ornaphthalene and a higher boiling product or bottoms product normallyutilized as a fuel oil stock. The cut point between the dealkylatedliquid fraction and the bottoms fraction depends upon the type of feedand the dealkylated product to be recovered. Where naphthalene is theprimary end product, the cut point should be about 400600 F., andideally between 440 and 525 F. The naphthalene product from thehydrodealkylation unit is preferably pumped to the preheater system at atemperature of about 250 F.

Hydrogen for the operation may be obtained from any one of a variety ofrefinery streams. For example, the hydrogen feed may be derived as anoff-gas from the hydrodealkylation unit or it may be obtained as anoff-gas from a reformer unit or the like. Whether derived from coalrefinery streams or petroleum refinery streams, the hydrogen willnormally contain extremely small amounts of sulfur contaminants. As willbe pointed out hereinafter in greater detail, it is necessary in thepresent process that the materials contacted by the hydrogenationcatalyst be substantially free of such sulfur contaminants. Accordingly,the hydrogen, containing small amounts of contaminating sulfur, may bemixed with the hydro dealkylation feed, which also contains smallamounts of contaminating sulfur, and then desulfurized as hereinafterpointed out; or, preferably, the hydrogen feed is caustic scrubbedbefore mixing with the feed. In any event, the hydrogen feed, at atemperature of about 200 F., is passed to the preheater along with thehydrodealkylation product.

It has been found in accordance with the present invention thathydrogen-to-hydrocarbon ratios may vary quite widely without seriousultimate eflect on the operation. Specifically, thehydrogen-to-hydrocarbon mole ratio may vary anywhere between about 6 and2'5 to 1. However, if the hydrogen-to-hydrocarbon ratio falls belowprudent limits, the reduced amount of hydrogen will decrease the partialpressure of hydrogen and, as pointed out hereinafter, decrease inpressure below desired limits will eventually result in mixed phaseoperation. Ultimately the selectivity of the catalyst for Tetralinproduction will be effected.

The preheating of the feed or, ultimately, the temperature at whichhydrogenation is carried out, has a rather profound effect upon thepresent process and to a great extent dictates the manner in which theprocess is operated. Specifically, it has been determined that thereaction should be carried out while maintaining a vapor phase at alltimes. lIf vapor phase operations are not carried out, it has been foundthat there is a tendency to produce Decalin rather than Tetralin andthere is the further tendency to lay down coke and polymers on thecatalyst. Hence, the feed material should be preheated to a temperatureof about 375 to 450 F, and preferably the upper temperature. By varyingthis preheating temperature within the range indicated, some flexibilityin throughput can be built into the system depending, of course, uponthe hydrogen-to-hydrocarbon ratio. 0n the other hand, it has also beenfound that excessive temperatures are detrimental to the selectivity andactivity of the hydrogenation catalyst. These phase and temperaturecharacteristics of the hydrogenation of naphthalene dictate, to acertain extent, the novel reactor system utilized in the presentinvention. The details of the novel reactor system and the temperaturedistribution therethrough will be discussed hereinafter.

The naphthalene feed, utilized in accordance with the present invention,will normally contain from about 1 to 50 ppm. of sulfur. Since thepresent process utilizes a sulfur-sensitive catalyst, as discussedlater, it is necessary that this small amount of sulfur be removed fromthe feed prior to the hydrogenation reaction. In accordance with thepresent invention, a wide variety of the materials were tested for theremoval of sulfur from the feed material. It was determined that thebest procedure was to utilize a chemisorptive material in a guard caselocated in advance of the first catalyst unit. It was further determinedthat this guard case material should have no hydrogenation activity ofits own; that it should have a high surface area; that it should have ahigh metal content and therefore a long life; that it should preferablybe reducible, for regenerative purposes, at the same temperature as thehydrogenation catalyst is pretreated; and that it should be effectiveunder conditions substantially the same as those utilized in the hydrogenation reaction itself. Among the materials found effective forpretreatment of the feed materials were iron in the form of powder or asiron filings, or on a suitable high surface area support. While the ironproved effective in the removal of sulfur from the feed, the temperaturerequired to reduce the iron was considerably above that required for thehydrogenation step. It was also found that pre-reduced nickel on asuitable support was effective for the removal of contaminants from thefeed. However, the pre-reduced nickel deposited on a suitable highsurface area support has a tendency to abrade and be carried over intothe catalyst units as fines. This abrasion, of course, causes a loss ofthe pretreating agent and thus, a loss in its activity for its intendedpurpose. The carry-over of reduced nickel also results in rapidselectivity deterioration as evidenced by substantial increases inDecalin production. A material found most outstanding for the removal ofcontaminating sulfur from naphthalene is copper oxide deposited on ahigh surface area support. More specifically, the pretreating agentshould contain about to of copper oxide on a suitable inert support. Amaterial of this character, containing 20% copper oxide, is designatedCu-0803T by its manufacturer, the Harshaw Chemical Company of Cleveland,Ohio. The following table shows the effectiveness of the copper oxide asa material for the removal of contaminating sulfur from the naphthalenefeed.

In all of the runs hereinafter reported, the factor K represents thehydrogenation catalyst activity and the factor K /K represents theselectivity of the catalyst to Equations 1 and 2 can be integrated toyield:

ONO

Reactor volume Volumetrie fiow rate (at reactor conditions) (5) Thefinal item needed to calculate the experimental rate constants is thehydrogen partial pressure. It is convenient to assume that this quantityis constant across the reactor by using an average reactor pressure.

Having 'r and 11' and the product composition permits calculation of theexperimental rate constants from Equations 3 and 4. K, can, of course,be calculated directly from Equation 3 and K is obtained bytrialand-error solution of Equation 4.

By way of illustration, at 99.5% conversion, a value of K /K of 25 willindicate a product of 0.005 (mol fraction) naphthalene, 0.838 Tetralinand 0.157 Decalin; of 250, 0.005 naphthalene, 0.978 Tetralin and .017Decalin; and of 2500, 0.005 naphthalene, 0.993 Tetralin and 0.002Decalin.

The conditions of operation and results are set forth in the tables.Table I shows the results of tests using 20% copper oxide on an inertsupport as a guard case and 10% nickel oxide on an inert support. Bothcontact agents were in the form of A3" pellets and the nickel oxide wasreduced with hydrogen at 600 F. prior to the tests.

TABLE I.-GUARD CASE STUDIES Time Hydrogen from partial Resldence Temp-Wt. percent Run start, pressure, time, erature, K No. hrs. WHSV,p.s.i.g. sec., F seer K /K Dccalin Tetralin Naphthalene 2. 3 5 2. 0 465l. 4 500 Tr 04.0 G. 0 1. 9 94 3. 0 465 1. 3 125 2. 2 05. 4 2. 2 1 1. 0100 3. 2 405 1. 2 125 2. 4 95. 0 2, 0 1. 2 2. 5 465 1. 0 5. 00 0. 2 00.5 .l. 3 1.3 49 2. 5 465 1.0 500 0.2 90.3 0. i 2 2. 0 64 3. 0 475 0. 247. 3 52, 7 2. 0 64 3.0 475 1. 3 6. 5 90. 7 1. 8 3 2. 0 64 3. 5 475 1. 036 6. 9 90.0 3, 1 2. 3 77 2. 0 475 1. 9 33 8. 9 88. 7 2. 4 1. 9 2. 1455 1. 6 770 0.3 96. 0 3. 7 4 2, 0 37 1. 4 458 l. 4 2, 000 Tr 85. 7 14.3 2.0 37 1.4 435 1. 7 2,000 T 91.6 8.4

K 1rC -K 1rC"r (2) Where:

C =Naphthalene mole fraction (hydrogen free basis) C =Tetralin molefraction (hydrogen free basis) t=Time, seconds 1r=Hydrogen pressure,atmospheres K K =Ratc constants The first, fourth and sixth tests, setout in Table I above, show the copper oxide guard performed well overshort test periods. In the fifth test, the conversion remained constantat 96 to 97% Tetralin at 100 hours. The test was terminated voluntarilyat hours. The sixth test was also conducted in a slightly larger reactorthan that of test 5, and it is apparent that the results confirm theprior test. Tests 1 through 4 and 6 show temperatures at a point outsidethe reactor and as a result the internal reactor temperatures wereslightly higher.

By contrast to these results, similar tests were conducted using thesame hydrogenation catalyst and at a weight hourly space velocity (WHSV)of 2, a temperature of 460 to 470 F. and a pressure of 60 p.s.i.g.However, no guard case was used. In a first test the unit was run withpure hydrogen for about eight hours and then with hydrogen containingsmall amounts of sulfur. The Tetralin percentage in the productdecreased suddenly. in several other tests in another reactor, thecatalyst was poisoned in about four hours (sharp decline in Tetralinproduction) even though pure hydrogen was used.

9 The treatment of the feed with the copper oxide should, of course,remove the contaminating sulfur at the operating conditions existent atthe entrance to the first reactor chamber. Specifically, the naphthalenefeed passes through the copper oxide guard case at a temperature at tentof the catalyst increases, the activity of the catalyst increases butits selectivity to the production of Tetralin decreases. Accordingly,one is faced with the activityselectivity dilemma, even with aconventional nickel Oxide catalyst. It has been found in accordance withthe about 375 to 450 F., and preferably at a pressure of 5 presentinvention that the catalyst should contain between about to 100 p.s.1.g.The effects of pressure in th about 0.5 and nickel oxide for bestresults. The present process will be discussed in greater detail whenmost desirable catalyst is one containing about 10% reference is made tothe operation of the hydrogenation nlckel, since it has been found thatsuch a catalyst has system. 10 approximately the sameactivity-selectivity properties as One of the 11121101 advantages. ofthe present invention is One Containing about n c and e gher Conthat itmakes possible the use of a readily-available, incentration will, ofcourse, permit longer catalyst life. A expensive hydrogenation catalystwith no sacrifice of catahighly effective catalyst in accordance withthe present lyst life, catalyst activity or selectivity for the produc-Invention is one designated Ni-O O T by its manufacturer, tion ofTetralln. As a matter of fact, as is pointed out 1 the Harshaw ChemicalCompany of Cleveland, Ohio. This hereinafter, the life, activity, andselectivity of the cataparticular catalyst can be regenerated bycalcination in lyst in the present process is vastly superior toanything air at a temperature of about 1100 F. heretofore suggested inthe prior art. Obviously, the least The previous Table I set forth somecatalyst life data expensive catalyst will be a known hydrogenationcatalyst and the following tables include additional catalyst life Whichis sulfur-sensitive but which could not have here- 20 data and data onthe activity and selectivity of catalysts tofore been used on sulfurcontaminated feeds. Howcontaining between about 0.5 and 25% of nickeloxide. In ever, by the use of the guard case in the present invention,each test of Table II, a 600 F.-8 hour reduction period it is possibleto utilize such sulfur-sensitive catalysts. An was used on thehydrogenation catalyst. A copper oxide ideal catalyst in accordance withthe present invention guard case was used at nominal operatingconditions of was found to be nickel oxide deposited on a high surface25 p.s.i.g., a WHSV of 1.5 to 2.0 and a H /HC ratio of area, inertcarrier. 8/1. Quinolin was added to the feed, where indicated inHowever, it has been found, in accordance wlth the Run 3, as a promoterfor the reaction. The data of Table present invention, that nickel oxidecatalysts cannot be III, below, were obtained with a copper oxide guardcase indiscriminately utilized even in the present inventlon. and anickel oxide catalyst, as previously noted, at a tem- For example, ithas been found that as the nickel con- 30 perature of about 440 F.,except as noted.

TABLE II Hydrogen Nickel partial Shell wt. percent content, pressure,Resldence tempera- K1, Run percent WHSV p.s.1. tune, sec. ture, F. seerDecalin Tetralin Naphthalene 1.7 56 1.9 455 1.9 3.0 94.2 2.3 1 25 1. 657 1. 6 475 1. 3 2. 2 92. 6 5. 2 1.6 57 1.5 495 1.6 1.2 90.3 3.5 1.6 531.7 455 1.9 1.6 94.3 3.6 2 15 1. 3 54 1. 6 475 1. 7 0. 5 93.2 6. 3 1. 455 1. 7 495 1. 3 0. 5 39. 4 10.1 1.9 55 2.1 455 1.6 0.3 96.0 3.7 2.0 371.4 453 1.4 0.0 35.7 14.3 3 10 2. 0 37 1. 4 435 1. 7 T1. 91. 6 3. 4 1.737 1.3 433 1.7 0.1 91.3 3.6 3.7 34 1.5 432 0.6 0.0 61.2 33.3 2.0 55 2.3455 1.5 0.7 96.0 3.2 4 3.6 1.3 56 2.3 475 1.2 0.2 94.1 5.6 2. 0 54 2. 3495 0. 9 Tr. 37. 4 12. 6 1 1. 3 55 1. 3 455 0. 7 Tr. 73. 9 26.1 5 0.5 1. 9 55 1. 3 475 0. 6 Tr 66. 4 33. 3 1. 7 54 1. 3 495 0. 5 Tr. 61. 933. 1

TABLE III Outlet Cumulative 1 H2 rate pressure, Residence K1,

lbs. feed s.c.f.h. p.s.i.g. time, sec. WHSV HQ/HC sec.- D D D-T T N 14.5 lbs. catalyst charge.

The used catalyst of Table III was successfully regenerated by calciningin air at 1100 F. Table IV compares the regenerated catalyst with newand spent catalyst.

The temperature at which the catalyst is reduced also has a bearing onthe selectivity of the catalyst. Table V, below, illustrates this.

passage to the next adiabatic reactor. This procedure is repeatedthrough all of the adiabatic reactors. The cooling units are preferablycooling units indirectly cooled with Dowtherm or another appropriatehigh-boiling cooling agent. The last reactor in the series is anisothermal reactor designed to complete the hydrogenation of thenaphthalene to a product containing in excess of 95% Tetralin. Theproduct from the last adiabatic reactor, at a temperature of about 550F. is, of course, cooled through the last cooler to the initial feedtemperature, for example 450 F. It is then fed through the tubes of atube and shell reactor, which tubes are filled with the nickel oxidesupported catalyst. Circulating between the tubes and the shell of thereactor is a suitable coolant such as the Dowtherm utilized in theadiabatic coolers. By way of specific example, the product of theisothermal reactor is discharged at a temperature of about 475 F. By wayof specific example, the reactor system for a 100,000,000 lb. per dayTetralin plant would include 4 TABLE V Average Catalyst Average Averagereactor Rate reduction reactor reactor pressure Hz/HC Residenceconstant,

temp, temp., pressure, drop, inlet time, K1, atmr Selectivity, F. F.p.s.i.g. p.s.i.g. conditions WHSV sec. hr.- Kl/KZ 1 Mixed Phase-productanalysis-100% Decalin. Z gonversion too low to permit accuratemeasurement of Decalm.

The catalyst is distributed exponentially throughout a series offixed-bed hydrogenation reactors. As will be pointed out, there arepreferably 5 to 8 such fixed-bed reactors connected in series and havingcooling units containing Dowtherm between each successive reactors.

As previously pointed out, the hydrogenation reaction is an exothermicreaction. Further, it has been found that excessive temperatures aboveabout 550 F. are detrimental to catalyst activity and selectivity.Finally, it has also been found that volumetric reaction rates fromnaphthalene to T etralin to Decalin preclude the operation of theprocess as an isothermal operation throughout. More specifically, it hasbeen found in accordance with the present invention that if thehydrogenation reaction is carried out through a series of adiabaticreactors without product separation and until a majority of thenaphthalene hydrogenation has taken place, and thereafter the finalportion of the naphtalene is hydrogenated in an isothermal reactor,extremely high selectivity to Tetralin can be attained. Still morespecifically, it has been found that if the hydrogenation of naphthaleneto Tetralin is carried to at least about 50% and preferably to about 80%completion, through a series of adiabatic reactors, the reaction rate issufliciently low in the hydrogenation of the remaining 8099% ofnaphthalene that an isothermal hydrogenation can then be carried out.Preferably, therefore, a seires of from 4 to 7 fixed beds operatedadiabatically and in series is utilized in accordance with the presentinvention. In each of these reactors, the temperature is permitted torise adiabatically by between 50 to 100 F. In a specific example, thefeed temperature to the first adiabatic reactor would be about 450 F.and the exit temperature about 550 F. Following each adiabatic reactoris a cooler adapted to cool the product from preceding reactor to theinitial feed temperature for diabatic reactors, comprising 2.5, 3.0, 4.0and 7-foot lengths, respectively, of 16" diameter pipe. These fourreactors would contain 250, 300, 400 and 700 pounds of catalyst each.Following each of the four adiabatic reactors, would be a cooler havingfrom 200-300 sq. ft. of Dowtherm exchanger surface. The isothermalreactor would include about 280 two-inch tubes, 10' in length andcontain 2800 pounds of catalyst.

As was also previously pointed out, it is quite critical to the presentinvention that the vapor phase be maintained throughout the reaction.Specifically, since naphthalene boils at about 425 F., reactortemperatures should be maintained above this value. It has been found inaccordance with the present invention that if mixed liquid and vaporphases exist in the reactors, this detrimentally affects the selectivityto Tetralin. The primary factors which determine whether such vapor ormixed phase shall exist are, of course, the temperature and the systempressure. Under the temperature conditions previously pointed out, ithas been found that hydrogen partial pressure throughout the systemshould be maintained between about 20 and p.s.i.g. If the pressure atthe temperatures indicated exceeds about 100 p.s.i.g., the selectivityto Tetralin decreases. Previous Table V shows the effect of reactiontemperature variations and/ or variations in pressure on conversion andselectivity. As noted, Run #1 was a mixed phase reaction due to the highpressure and conversion was too low to measure in the high temperatureRun #4. Runs designated 7-24 and 7-25 of previous Table III also showthe effects of increasing the temperature from previous temperature of440 F. to 480 F. and 548 F., respectively.

As indicated by the previous data and as previously indicated, the onlyreal effect of pressure on the reaction is to change selectivity toTetralin by changing the volicity and the rate of axial dispersion (lowvelocities encourage channeling and stagnant regions) and creating mixedphase conditions which result in drastic changes in residence time andreaction mechanism. To illustrate this, the following Table VI setsforth low pressure Runs 1,

14 hydrogenation catalyst is a sulfur-sensitive hydrogenation catalyst.

5. A method in accordance with claim 4 wherein the sulfur-sensitivehydrogenation catalyst is nickel oxide deposited on an inert, solidsupport.

2 and 3 and selected runs from previous Table HI. 5 6. A method inaccordance with claim 1 wherein the hy- TABLE VI Pres- Temp., sure, Onin CN out On N t sec. p.s.i.g Hz/HC WHSV K1 N orn.0atalyst activitydecreasing with time.

Accordingly, operation at a nominal inlet pressure of drogenationcatalyst is an oxide of a hydrogenation metal 100 p.s.i.g. isrecommended. This pressure is sufliciently and said oxide is at leastpartially reduced prior to reactlow to prevent mixed phase operation andsufliciently ing the naphthalene with hydrogen. high to permit anoverall weight hourly space velocity 7. A method in accordance withclaim 1 wherein the (WHSV) of about 2. hydrogenation conditions aresufiicient to maintain sub- While it was observed that increasing thehydrogen-tostantially all of the reactants and products in the reactionhydrocarbon ratio appears to increase reaction rate by zones in avaporphase. some complex diffusion mechanism, this ratio is not highly 8. Ina method of producing tetrahydronaphthalene by critical. Increasing theHg/HC ratio from 6/1 to 25/1 reacting naphthalene with hydrogen, theimprovement increases the hydrogen partial pressure by less than aboutcomprising; passing at least said naphthalene through a 10% and aspreviously indicated only extreme variations body of a particulatematerial comprising copper oxide inreaction pressure alfect the result.As a practical matter, deposited on a solid, inert support andthereafter said a ratio of 6/1 to 25/1 should be used. hydrogen withsaid naphthalene in the presence of a The weight hourly space velocityin the reactor is also sulfur-sensitive hydrogenation catalyst and underhynot a particularly critical factor over practical limits. Fordrogenation conditions. example, a suitable weight hourly space velocityshould 9. A method in accordance with claim 8 wherein the be betweenabout 0.5 and 2.5. It has been found that if the reaction is conductedunder adiabatic conditions until at weight hourly space velocity is toohigh above 2, for least about of the naphthalene is converted totetraexample between 2 and 4, this factor begins to influencehydronaphthalene, and the conversion of said naphthalene the conversion.Table VII illustrates the effect of varying to tetrahydronaphthalene isthereafter carried to substan the WHSV. tial completion under isothermalconditions.

TABLE VII Pressure, Temp, Time, K1, Test WHSV p.s.i.g. H2/HC F. sec.sec.- D T N The weight hourly space velocity through the guard case 10.In a method of producing tetrahydronaphthalene can be lower than throughthe reactors, for example beby reacting a sulfur-containing naphthalenewith hydrogen, tween about 1.0 and 1.5. 50 the improvement comprising;passing at least said naph- Having described and illustrated the presentinvention thalene through a body of a particulate material comprisbyspecific examples and comparisons and a specific flow ing copper oxidedeposited on a solid, inert support and diagram, it is to be understoodthat these are not to be thereafter reacting said hydrogen with saidnaphthalene in considered limiting but the present invention is to bethe presence of a sulfur-sensitive hydrogenation catalyst limited onlyin accordance with the appended claims. in a plurality of seriallyconnected reaction zones contain- We claim: ing a hydrogenation catalystwhile maintaining hydrogena- 1. A method for producingtetrahydronaphthalene, tion conditions therein and while maintainingsaid naphcomprising; reacting naphthalene and hydrogen in a pluthalenein the vapor phase, at least a first of said reaction rality ofserially-connected reaction zones containing a zones being maintainedunder adiabatic conditions and hydrogenation catalyst while maintaininghydrogenation below about 550 F., and at least the last of said reactionconditions therein and while maintaining said naphthalene zones beingmaintained under isothermal conditions and in the vapor phase, at leasta first of said reaction zone below about 550 F. being maintained underadiabatic conditions and below 11. A method in accordance with claim 10wherein the about 550 F. and at least the last of said reaction zoneshydrogenation catalyst is nickel oxide deposited on a solid, beingmaintained under isothermal conditions and below inert support. bout 550F, 12. A method in accordance with claim 10- wherein the 2. A method inaccordance with claim 1 wherein the hydrogenation catalyst is an oxideof a hydrogenation reaction is carried out in the adiabatic reactionzones until metal and said oxide is at least partially reduced prior toat least about 50% of the naphthalene has been converted reacting thenaphthalene with hydrogen. to tetrahydronaphthalene. 13. A method inaccordance with claim 10 wherein the 3. A method in accordance withclaim 1 wherein at reaction is carried outin the adiabatic reactionzones until least the naphthalene is contacted with a particulate matetleast about 50% of the naphthalene has been converted rial comprisingcopper oxide on an inert, solid support to tetrahydronaphtha1ene priorto reacting said naphthalene with hydrogen.

4. A method in accordance with claim 3 wherein the (References onfollowing page) 15 16 References Cited 3,344,200 9/1967 Wold 260-667UNITED STATE PATENTS 1,921 9/ 1949 Gwynn 26Q667 10/1929 schrauflsl 260667 1, 4/1935 Speer 2 7 2/1969 Zulueta 27,7 1/1966 le 260-667 g; 32% {13 5 DELBERT E. GANTZ, Primary Examiner OI! 9 19 1 s fj f: 2' 0 7 V.OKEEFE, Assistant Examiner 2/ 1966 Deu Herder 260-667 10/1966 Poll260-667 CL 6/1968 Craig et al. -1 260-667 10 20856 9/1968 Heuke et a1260667

